This invention relates to reactive agents for olefinically unsaturated polymers. More particularly, this invention relates to the coupling, crosslinking or chemical modification of polymers containing an unsaturated linkage wherein the polymer is reacted with an organic compound containing at least one oxycarbonylsulfenyl chloride group, that is, one --OC(:O)SCl group.
Weiss et al. in German Published Application No. 1,568,632 disclose the reaction of certain alcohols with chlorocarbonyl sulfenyl chloride to form compounds which are useful in the present invention.
Numerous methods are known in the art for crosslinking unsaturated polymers, particularly the crosslinking of the elastomeric diene rubber hydrocarbon polymers. However, it is always desirable to provide more efficient chemical crosslinking agents, particularly for use in connection with the crosslinking of polymers having only a limited number of olefin sites available. It is also desirable to provide organic chemical modification agents which allow the facile introduction of reactive functional groups into olefin-containing polymers. Such more effective crosslinking agents are especially suitable in connection with the coupling of unsaturated polymers having unsaturation only at the end of the chain, since these polymers are typically less susceptible to crosslinking agents.
In accordance with the present invention, there has been discovered a method for coupling, crosslinking or chemically modifying olefinically unsaturated polymers which comprises reacting the polymer at the site of olefinic unsaturation with an aliphatic oxycarbonylsulfenyl chloride represented by the general formula R(OC(:O)SCl).sub.n prepared by reacting an alcohol or polyol with chlorocarbonyl sulfenyl chloride, where n is an integer of one or more and R represents a saturated aliphatic radical, being the residual portion of a monohydric or polyhydric alcohol or a polyalkylene ether polyol. R may contain substituent groups as defined herein.
The olefin-reactive compounds of the present invention are employed in two basic reactions, depending on their functionality, chemical modification or crosslinking. When employed as chemical modification agents, without crosslinking being desired, the reactive compounds of the present invention will have the formula R--OC(:O)SCl, R representing a saturated organic aliphatic radical, preferably of from 1 to 12 carbon atoms. Since the olefin addition reaction proceeds by addition of the --SCl moiety of the aliphatic oxycarbonylsulfenyl chloride to the olefinic linkage, a functional group may be present in the R radical, provided it is non-reactive or compatible with the --OC(:O)SCl group, and the olefin polymer is thereby modified by introduction of such functional groups. A particularly preferred embodiment resides in the hydroxy-functionalization of olefin polymers by providing compounds where R is hydroxy-alkyl, especially C.sub.1 to C.sub.12 hydroxy alkyl. This allows polymers to be prepared having one or more pendant --OH functional groups. The polymers thereby become suitable for reaction with species such as polyisocyanates to form urethane reaction products, either rigid or flexible foams or elastomers, which have a variety of structural and insulation uses, as is well known to those in the polyurethane field. Chemical modification may be combined with crosslinking when the reactive agents of the present invention are used in polyfunctional form as described hereinbelow.
When employed in the preferred embodiment comprising crosslinking reactions, the aliphatic oxycarbonylsulfenyl chloride compounds of the present invention will be employed in polyfunctional form and may therefore be represented by the general formula R(OC(:O)SCl).sub.n where n is an integer of at least 2 and preferably 2 to 3. When n is 2, that is, when two olefin-reactive oxycarbonylsulfenyl chloride groups are present, the compounds of the present invention will serve as a crosslinking moiety between two unsaturated polymer molecules. If three or more of such reactive groups are present, the crosslinking agents can link three or more sites of olefinic unsaturation at a single coupling point and thereby allow for the formation of network polymer systems, even if the unsaturated polymer has only two olefin sites.
Chemical modification may be combined with crosslinking in accordance with the present invention. Thus, the R radical of the general formula R(OC(:O)SCl).sub.n may be a simple unsubstituted alkyl group or it may be a substituted alkyl group, the substituents being functional groups such as hydroxyl, chloro, nitro, oxy, oxycarbonyl or a C.sub.1 -C.sub.4 alkyl or alkoxy-substituted silyl group. The R radical should not contain any olefinic unsaturation since undesirable side reactions may result. Functional groups, such as amino or epoxy, which may react with the oxycarbonylsulfenyl chloride should not be present. Particularly useful are mono- and polyhydroxy substituted alkyl radicals, since these compounds provide a means by which a reactive hydroxyl functional group or groups may be incorporated into a crosslinked polymer system. Such crosslinking agents, particularly where the R group contains 1 or 2 --OH substituents and n is 2 or 3, constitute a preferred embodiment of the present invention.
The crosslinking and chemical modification agents of the present invention may be prepared by reacting chlorocarbonylsulfenyl chloride, ClSC(:O)Cl, with an appropriate hydroxyl-containing aliphatic compound such as a monohydric or polyhydric alcohol or a polyalkylene ether polyol whereby a monofunctional or polyfunctional crosslinking or chemical modification agent of the general formula R(OC(:O)SCl).sub.n is obtained. Preferred embodiments comprise agents prepared from monohydric or polyhydric alcohols having 1 to 12 carbon atoms wherein n is an integer of 1 to 3, indicating the number of hydroxyl groups replaced by the --SC(:O)Cl moiety. Examples of such monohydric or polyhydric alcohols are ethanol, propanol, butanol, amyl alcohol, ethylene glycol, diethylene glycol, propanediol, glycerol, trimethylol propane and the like. Ethylene glycol is particularly useful since a desirable hydroxy substituted olefin-reactive agent of the formula HOCH.sub.2 CH.sub.2 OC(:O)SCl may be readily prepared by reaction with chlorocarbonyl sulfenyl chloride in equimolar amounts and is believed to constitute a novel compound.
Suitable polyalkylene ether polyols for reaction with ClSC(:O)Cl to prepare chemical modification and crosslinking agents useful in the present invention are those polymeric polyols prepared from alkylene oxides having 2 to 5 carbon atoms such as ethylene oxide, propylene oxide, butylene oxide, amylene oxide and the like and C.sub.2 -C.sub.12 polyols such as ethylene glycol, propylene glycol, glycerol, trimethylol propane and the like, the polyol having about 2 to 3 hydroxyl groups. Generally, these polyalkylene ether polyols contain 5 to 30 moles of alkylene oxide per hydroxyl group. Examples include polyethylene ether glycol, polypropylene ether glycol and polybutylene ether glycol. Particularly preferred are polyethylene glycols and polypropylene glycols of molecular weight about 200 to 2000.
Polyfunctional crosslinking agents of the present invention may be prepared by reacting a monofunctional compound such as hydroxy substituted aliphatic oxycarbonylsulfenyl chloride with additional chlorocarbonyl sulfenyl chloride whereby a bis-sulfenyl chloride compound having the following formula is formed: ClS(O:)CO--(CH.sub.2 CH.sub.2)--.sub.n OC(:O)SCl; in the alternative a difunctional compound could be prepared by reacting an appropriate diol such as 1,3-propanediol with a molar excess of chlorocarbonyl sulfenyl chloride whereby 1,3-propane-bis-oxycarbonylsulfenyl chloride is formed. Polyfunctional compounds are prepared generally by providing 1 mole of chlorocarbonyl sulfenyl chloride for each hydroxyl group in the polyhydric alcohol or polyol.
The crosslinking agents of the present invention find particular utility in the preparation of crosslinked elastomeric foams, since gaseous HCl liberated as a by-product of this crosslinking reaction under certain conditions when the polymer contains trisubstituted olefinic carbon atoms as explained in detail below. For example, a crosslinked butyl rubber (isoprene-isobutylene copolymer) foam may be prepared by reacting the butyl rubber elastomer with the crosslinking agent at room temperature, and such crosslinked foams constitute a further embodiment of the present invention. The HCl gas serves as an in situ blowing agent in the production of such foams.
The chemical modification and crosslinking agents of the present invention are employed in stoichiometric proportions relative to the quantity of unsaturated polymer being treated. For each equivalent of reactive olefinic linkage there will be used one equivalent --OC(:O)SCl group. Thus, a typical crosslinking reaction would employ one mol of a difunctional compound of the formula R(OC(:O)SCl).sub.2 for every two equivalents of unsaturation in the crosslinkable olefin-containing polymer.
A wide variety of olefin-containing polymers may be crosslinked or chemically modified in accordance with the present invention. It has been found that the alkoxycarbonylsulfenyl chloride crosslinking agents of the present invention exhibit high efficiency in their reaction with the olefinic structure and are effective even when the polymer is a low unsaturation polymer such as a polymer which contains only two olefinic linkages per molecule. Thus, the invention has general applicability to olefin-containing polymers.
The following categories of unsaturated polymers are within the scope of the present invention.
Synthetic and natural rubber hydrocarbon elastomers such as natural rubber, synthetic polyisoprene rubber, styrene-butadiene rubber, butadiene-acrylonitrile rubber, butadiene-acrylic acid copolymers, polybutadiene rubber, polyisobutylene, ethylene propylene copolymers and terpolymers (EPDM), butyl rubber, polychloroprene and similar elastomers derived from 1,3-dienes. Reactions with these elastomers constitute preferred embodiments, particularly reactions with low unsaturation elastomers such as butyl rubber or EPDM polymers. The term "EPDM" is used herein as defined in ASTM-D-1418-64 and is intended to mean a terpolymer containing ethylene and propylene in the backbone and a diene, such as ethylidene norbornene, in the side chain. Butyl rubber refers to copolymers of isoolefins and conjugated dienes which comprises about 0.5 to about 15 mole % conjugated diene and about 85-99.5% isoolefin.
Other suitable polymers are the vinyl and vinylidene polymers such as the styrene polymers which include unsaturated copolymers of styrene with other vinyl monomers, polymers of derivatives of styrene and mixtures of polystyrene and styrene-containing copolymers with elastomers, such as copolymers with acrylonitrile and copolymers with fumaronitrile, fumarate esters and maleic anhydride, blends or copolymers of polystyrene or styrene-acrylonitrile copolymers with an elastomer such as a butadiene-acrylonitrile copolymer (ABS resins).
Also suitable are the olefinically unsaturated acrylic polymers such as poly(methacrylate) and higher alkyl methacrylate polymers and polyacrylonitrile.
Also suitable are the polyvinyl ester and related polymers such as polyvinyl acetate and copolymers thereof such as ethylacrylate copolymers. Other vinyl polymers as exemplified by poly(vinyl carbazole), poly(vinyl oxazolidinone), polyvinyl ethers, polyvinyl ketones, and coumaroneindene resins.
Also suitable for use in the present invention are the unsaturated polyester resins in which the di-basic acid or the glycol contain olefinic unsaturation, such as polyesters based on maleic anhydride or fumaric acid and ethylene or propylene glycol. These unsaturated polyester resins generally also contain a vinyl monomer such as styrene. Also suitable are allyl resins and polymers derived from esters of alcohol and di-basic acids such as diallyl phthalate and diallyl isophthalate, as well as the allyl carbonate resins. Also suitable are the alkyd resins which are unsaturated polyesters in which the alkene linkage resides in a fatty acid component such as oleic acid or linoleic acid. The crosslinking agents of the present invention may also be used for modification of polyolefins and polysiloxanes containing a pendant vinyl group such as polyethylene and polymethylsiloxane or polyphenylmethylsiloxane.
Also suitable are the polyepoxide compounds including polymers and copolymers of epoxy-containing monomers possessing at least one polymerizable ethylenic linkage as exemplified by poly(allyl 2,3-epoxypropyl ether), allyl 2,2-epoxypropyl ether styrene copolymer and poly C.sub.4 -glycidyl oxystyrene.
Further embodiments of the present invention constitute the addition products of the aforesaid olefin-containing polymers with the aliphatic oxycarbonylsulfenyl chloride compound.
It should be noted that the addition reaction will proceed at different rates and with somewhat different final products depending upon the structure of the olefin-containing polymer being treated in accordance with the present invention. Generally speaking, these products may be described as chemically modified (including crosslinked) derivatives of olefinically unsaturated polymers, the polymer being modified by addition thereto at the site of olefinic unsaturation of an aliphatic organic oxycarbonylsulfenyl chloride compound having the formula R(OC(:O)SCl).sub.n, n being an integer of at least 1, and preferably 2 to 3, said polymer having at least one olefinic linkage reactive with said aliphatic organic oxycarbonylsulfenyl chloride compound.
It has been found that if the polymer being treated in accordance with the present invention is a rubber hydrocarbon elastomer containing a trisubstituted or tetrasubstituted olefin then dehydrochlorination may also occur as part of the overall addition reaction with attendant loss of HCl taking place and formation of another adjacent olefinic carbon atom linkage as a consequence of the dehydrochlorination. Such a reaction sequence may be generalized by the following equation: ##STR1## In the above equation R.sub.1, R.sub.2, R.sub.3 are alkyl groups and R.sub.4 is alkyl or hydrogen.
In other instances when the olefin is usually mono- or disubstituted and sometimes even when trisubstituted, the addition reaction may proceed by addition of a chlorine atom to one olefinic carbon atom and the addition of the rest of the aliphatic oxycarbonylsulfenyl radical to the other olefinic carbon atom by linkage with the sulfur moiety. The product of this addition reaction may be represented as follows: ##STR2##
The present invention, therefore, comprises both polymeric products crosslinked or chemically modified at the site of olefinic unsaturation by either of the aforedescribed generalized structures. As noted above, crosslinked products require, by definition, the use of a polyfunctional oxycarbonylsulfenyl chloride compound, that is, one in which n represents an integer of 2 to 4, but n may be greater such as up to about 6 to 8.
Preferred embodiments constitute chemically modified or crosslinked derivatives of the hydrocarbon rubber diene elastomeric polymers, particularly low unsaturation polymers such as EPDM or butyl rubber.
The formation of stable adducts by the reaction of equimolar proportions of C.sub.2 to C.sub.12 polyols, the polyols being alkanediols or triols such as ethylene glycol, glycerol, hexanediol, hexanetriol, diethylene glycol, triethylene and tetraethylene glycol, trimethylol propane, dodecanediol and the like having the formula R'(OH).sub.a, a=2 or 3, R' being the C.sub.2 -C.sub.12 alkyl portion and chlorocarbonyl sulfenyl chloride is considered to be a further embodiment of the present invention, that is, such adducts are believed to constitute novel compositions of matter. Adducts with ethylene glycol, glycerol and trimethylol propane (TMP) are preferred. It is surprising, for example, that ethylene glycol and chlorocarbonyl sulfenyl chloride will react in a 1:1 molar ratio to form 2-hydroxyethoxylcarbonyl sulfenyl chloride, a stable product having the formula HOCH.sub.2 CH.sub.2 OC(:O)SCl in appreciable yields, such as the yield of about 70%, as demonstrated by the results of Example 2(a). With triols, such as glycerol and TMP, one of the hydroxyl groups will undergo reaction with an equimolar amount of ClC(:O)SCl.
The aforesaid stable adducts may be generalized by the following formula: (HO).sub.a R'--OC(:O)SCl where a is 1 or 2 and R' represents the alkyl portion of the polyol.
Weiss et al in W. German Offenlegungsschrift No. 1568632 (Published Mar. 19, 1970) make no mention whatsoever of the possibility of formation of the 1:1 equimolar adduct with ethylene glycol and specifically disclose at page 3 that when bifunctional alcohols are used the quantity of chlorocarbonyl sulfenyl chloride is increased correspondingly so that the amount is double the quantity used for a reaction with a monohydric alcohol.